Response of remission lymphocytes to autochthonous leukaemic myeloblasts

Lack of correlation between lymphocyte activating determinants and HLA-DR on acute leukaemias

The expression of allogenic lymphocyte-activating determinants (LAD) on 25 acute leukaemias has been compared with the expression of cell-surface antigens identified by HLA-DR allo- and xeno-antisera. The close correlation between LAD and DR known to occur on normal lymphocytes was not found in leukaemias. Twenty-two LAD+ leukaemias included 2 DR- cases, whilst 2 LAD- leukaemias were DR+. With the exception of 3 leukaemias all were strongly beta 2 microglobulin+. No correlation was found between the % DR+ cells and the level of lymphocyte stimulation. Separation of leukaemia cells on Ficoll gradients into fractions containing different proportions of DR+ cells did not correlate with LAD expression. Furthermore, antisera to DR antigens only partially blocked leukaemic LAD. The results support the notion that LAD on acute leukaemias are not necessarily associated with or identical to HLA-DR antigens, and that the lymphocyte activating capacity of HLA-DR may be modulated.

Immunotherapy versus chemotherapy of acute myeloid leukemia: response to PHA, allogeneic lymphocytes, and leukemic myeloblasts of remission lymphocytes from leukemia patients

Lymphocytes were studied from 51 patients with acute myeloid leukemia (AML) in remission given chemotherapy (CT) maintenance alone or given chemoimmunotherapy (CIT) with BCG and viable allogeneic leukemic cells. CT lymphocytes reacted significantly more to PHA (P less than 0.05) if taken later than 100 days after remission than if taken earlier. CIT lymphocytes reacted less. Thus, the late CT lymphocytes reacted significantly more to nonspecific stimulators (PHA and allogeneic lymphocytes, P less than 0.01) than did late CIT lymphocytes or control lymphocytes. In consequence, the ratio of reactions to specific (leukemic myeloblasts) over nonspecific stimulators was significantly higher in CIT (P less than 0.01) than in CT lymphocytes. Results may indicate nonspecific immunostimulation during CT, and also some relative specific sensitization to allogeneic myeloblasts during CIT.

Suppression of lymphoproliferative responses to alloantigens by autologous AML cells

Autologous acute myeloid leukaemia (AML), cells caused the suppression of incorporation of 3H-thymidine (3H-Tdr) by remission lymphocytes stimulated with allogeneic cells. In five patients, autologous AML cells suppressed 3H-Tdr uptake by lymphocytes stimulated with up to three different allogeneic cells. Responses to allogeneic AML cells were more strongly suppressed than responses to pooled allogeneic lymphocytes. Suppression was abolished by ultrasonic disintegration of the autologous AML cells, suggesting that a soluble factor was not involved. Suppression was absent from autologous AML cells exposed to ultraviolet light, or when untreated autologous AML cells were present in ratios of less than 1:1 to lymphocytes, or when added 24 or more hours after stimulation of remission lymphocytes with allogeneic cells. It is suggested that suppression is a property of the differentiative level of AML cells, rather than of their malignant properties, although malignant-transformation may bring AML cells into contact with circulating T cells in vivo. Autologous AML cells seem to interfere with the recognition phase of T cell function.

Surface antigens in acute myeloblastic leukaemia: a study using heterologous antisera

This study analyses the activity of 95 antisera raised in rabbits against human leukaemic myeloblasts. A number of different means were used to immunize both normal rabbits and rabbits which had been treated to render them tolerant of normal human splenic leucocytes. Different immunization schedules included the use of different doses of untreated myeloblasts, as well as myeloblasts treated with neuraminidase, antibody against human spleen cells or glutaraldehyde. Analysis of the sera was carried out using two sensitive techniques for detecting cell surface antigens: a radioactive anti-immunoglobulin binding assay using 125I-horse-F(ab')2-anti-rabbit-Fab and a K-cell-mediated cytotoxicity test using rat spleen cells as effectors. (i) The unabsorbed sera showed similar mean titres against leukaemic myeloblasts and normal splenocytes. (ii) Extensive absorption with pooled cadaveric spleen were required to remove antibody against polymorphic antigens. (iii) 17/95 antisera had activity against at least some leukaemic myeloblasts after extensive absorption with cadaveric spleen. (iv) Some of the 17 absorbed sera with selective activity for myeloblasts also reacted against PHA-induced lymphoblasts. (v) Although the 17 absorbed sera showed little or no activity against marrow in the above assays normal human marrow totally absorbed all residual activity in these sera against leukaemic myeloblasts. We conclude that although these sera contain activity against antigens common to leukaemic myeloblasts and a minority population of normal marrow cells, they have no detectable activity against leukaemic-specific antigens.

Stimulation of human lymphocytes in vitro by leucocytes from patients with untreated acute myeloid leukaemia

Leucocytes from sixteen untreated acute myeloid leukaemia (AML) patients were tested for their ability to stimulate lymphocytes from each of twelve normal donors. Of 192 tests between the stimulating AML leucocytes, and responding lymphocytes, 42% resulted in positive lymphocyte stimulation, in contrast to one-way mixed lymphocyte culture (MLC) responses, involving the same lymphocyte donors, which were 100% positive. Lack of stimulation by AML leucocytes was significantly associated, in 11% of the tests, with two or more HLA-A and/or -B antigens common to the responding lymphocyte and stimulating AML leucocyte. The most stimulatory of the AML leucocytes were obtained from two high-leucocyte-count acute myelomonocytic leukaemia patients. The stimulatory capacity of AML leucocytes did not correlate with the clinical fate of the cell donor. Presence of contaminating lymphocytes from the patient in the AML leucocyte samples did not account for the differences in stimulatory capacity between AML leucocytes. Limited in vitro viability of AML leucocytes was ruled out as a factor causing poor lymphocyte stimulation. Kinetic studies showed that AML leucocytes induce either an MLC-type response, or no response at all. Differences in response kinetics were observed between two normal and two remission AML patients, the latter receiving active immunotherapy. Pronase treatment of AML leucocytes failed to increase their stimulatory capacity, but distilled H₂O markedly reduced it. The significance of the results is discussed in relation to lymphocyte stimulation by other types of allogeneic cell, and in the context of active immunotherapy of AML.